1. Field of the Invention
The invention relates to a switching matrix for an input device such as a keyboard or a cursor device for the detection of various switching states. Particularly, the invention relates to a switching arrangement for the detection of the switching signals when two switching elements of a keyboard are synchronously pressed.
2. Related Technology
To operate electronic products, such as computers often requires input devices equipped with a number of keys, or switching elements, respectively Actuating these pre-assigned or freely configurable switching elements triggers electronic signals, which are processed by a microcontroller and then transformed into an operation desired by a user.
Not rarely, more than one of the keys of the keyboard are accidentally or deliberately pressed at the same time, which leads to problems detecting the switching signals, which possibly superimpose. The state-of-the-art knows various solutions to detect the switching states of synchronously actuated switching elements demanding more or less technical effort.
From U.S. Pat. No. 6,020,833 a process and an interface for the detection of switching states of keys and resistors of a keyboard are known. The interface includes a unit with several input and output lines. Some of the input and output lines are coupled with the switching lines, in order to establish a switching matrix. Switching elements are placed at nodes of the switching lines and the output lines, and between a switching line and an output line and associated resistor is placed.
Further, from U.S. Pat. No. 4,607,251 a system for the detection of closed contacts of a reed-like switch is known. In this system the switching elements are connected in parallel with the resistors to increase the electric potential of the switching lines. These switching elements are suitable to acceleratingly rotate the electric potential of the switching lines. In this way closed contacts can be correctly detected when the operational speed is increased.
In U.S. Pat. No. 5,448,236 a circuit for the detection of several synchronously pressed keys is disclosed. Hereby, the circuit consists of a number of switching elements that are matrix-like connected to a number of output lines and control lines by switching lines. Each switching element has a series-connected additional resistor. Additionally, each output line is connected to a device for the measurement of the electrical current.
Common to the above mentioned inventions is the not insignificant demand of electric components to reduce the required input and output lines.
The problem of the invention is to develop a switching matrix for the detection of switching states of one, two or more synchronously actuated switching element(s) that requires less input and output lines for the microcontroller and can be manufactured cost-effectively.